P1 and NR1 plasmid replication during the cell cycle of Escherichia coli

Replication patterns of the miniP1 plasmid pZC176, the miniNR1 plasmid pRR933, and the high-copy miniNR1 derivative pRR942 were examined during the Escherichia coli cell division cycle and compared to the cycle-specific replication pattern of a minichromosome and the cycle nonspecific pattern of pBR322. In E. coli cells growing with doubling times of 40 and 60 min, the miniP1 plasmid was found to replicate with a slight periodicity during the division cycle. The periodicity was not nearly as pronounced as that of the minichromosome, was not affected by the presence of a minichromosome, and was not evident in cells growing more rapidly with a doubling time of 25 min. Both miniNR1 plasmids, pRR933 and pRR942, replicated with patterns indistinguishable from that of pBR322 and clearly different from that of the minichromosome. It is concluded that both P1 and NR1 plasmids can replicate at all stages of the cell cycle but that P1 displays a slight periodicity in replication probability in the cycle of slower growing cells. This periodicity does not appear to be coupled to a specific age in the cycle, but could be associated with the achievement of a specific cell mass per plasmid. During temperature shifts of a dnaC(Ts) mutant, the miniP1 plasmid and pBR322 replicated with similar patterns that differed from that of the minichromosome, but were consistent with a brief eclipse between rounds of replication.

Creation of genome-wide protein expression libraries using random activation of gene expression

Here we report the use of random activation of gene expression (RAGE) to create genome-wide protein expression libraries. RAGE libraries containing only 5 x 10(6) individual clones were found to express every gene tested, including genes that are normally silent in the parent cell line. Furthermore, endogenous genes were activated at similar frequencies and expressed at similar levels within RAGE libraries created from multiple human cell lines, demonstrating that RAGE libraries are inherently normalized. Pools of RAGE clones were used to isolate 19,547 human gene clusters, approximately 53% of which were novel when tested against public databases of expressed sequence tag (EST) and complementary DNA (cDNA). Isolation of individual clones confirmed that the activated endogenous genes can be expressed at high levels to produce biologically active proteins. The properties of RAGE libraries and RAGE expression clones are well suited for a number of biotechnological applications including gene discovery, protein characterization, drug development, and protein manufacturing.

Cell-cycle research with synchronous cultures: an evaluation

The baby-machine system, which produces new-born Escherichia coli cells from cultures immobilized on a membrane, was developed many years ago in an attempt to attain optimal synchrony with minimal disturbance of steady-state growth. In the present article, we put forward a model to describe the behaviour of cells produced by this method, and provide quantitative evaluation of the parameters involved, at each of four different growth rates. Considering the high level of selection achievable with this technique and the natural dispersion in interdivision times, we believe that the output of the baby machine is probably close to optimal in terms of both quality and persistence of synchrony. We show that considerable information on events in the cell cycle can be obtained from populations with age distributions very much broader than those achieved with the baby machine and differing only modestly from steady state. The data presented here, together with the long and fruitful history of findings employing the baby-machine technique, suggest that minimisation of stress on cells is the single most important factor for successful cell-cycle analysis.

The radiographic quantitation of aortic valve calcification: implications for assessing bioprosthetic valve calcification in vitro

Calcification of natural aortic and bioprosthetic heart valves is a poorly understood phenomenon that results in valvular obstruction and tissue failure. We describe a non-destructive quantitative computed microtomographic (QCT) technique for determining both calcium content and local calcium distribution within explanted valves. As a reference standard, a dual-energy x-ray absorptiometry (DEXA) system with an accuracy demonstrated to be within 1% of the true calcium mass of test material was used to obtain the total calcium content of 24 human aortic valve cusps recovered at autopsy from patients aged 51-80 years. These cusps were then scanned using our unique volume QCT scanner, with multiple x-ray projections acquired by rotating the explanted tissue through a single axis of rotation. A three-dimensional cross-sectional map was reconstructed for each cusp. Voxel size was 0.003 mm3 and a calibration phantom was used to calculate calcium content. The minimum detection limit for calcium mass was 1 mg within the whole cusp. The DEXA and QCT scans were compared with respect to total calcium content, which ranged from 0 to 15 mg. An excellent correlation between the two independent techniques was demonstrated with an r2 value of 0.94 (p < 0.001). Non-destructive microtomographic CT scanning provided excellent volumetric density measurements, with quantitative 3D images permitting an assessment of any individual area of the cusp for calcium content and spatial distribution. This new approach to valve tissue analysis allows for subsequent histologic assessment.

Surface geometric analysis of anatomic structures using biquintic finite element interpolation

The surface geometry of anatomic structures can have a direct impact upon their mechanical behavior in health and disease. Thus, mechanical analysis requires the accurate quantification of three-dimensional in vivo surface geometry. We present a fully generalized surface fitting method for surface geometric analysis that uses finite element based hermite biquintic polynomial interpolation functions. The method generates a contiguous surface of C2 continuity, allowing computation of the finite strain and curvature tensors over the entire surface with respect to a single in-surface coordinate system. The Sobolev norm, which restricts element length and curvature, was utilized to stabilize the interpolating polynomial at boundaries and in regions of sparse data. A major advantage of the current method is its ability to fully quantify surface deformation from an unstructured grid of data points using a single interpolation scheme. The method was validated by computing both the principal curvature distributions for phantoms of known curvatures and the principal stretch and principal change of curvature distributions for a synthetic spherical patch warping into an ellipsoidal shape. To demonstrate the applicability to biomedical problems, the method was applied to quantify surface curvatures of an abdominal aortic aneurysm and the principal strains and change of curvatures of a deforming bioprosthetic heart valve leaflet. The method proved accurate for the computation of surface curvatures, as well as for strains and curvature change for a surface undergoing large deformations.

Effect of oxiplex* films (PEO/CMC) on adhesion formation and reformation in rabbit models and on peritoneal infection in a rat model

OBJECTIVE

To assess the efficacy of Oxiplex (FzioMed, Inc., San Luis Obispo, CA) barriers.

DESIGN

Film of polyethylene oxide and carboxymethylcellulose (Oxiplex) were tested for strength and tissue adherence. Films were selected for evaluation in models for biocompatability and adherence. Three films were selected for evaluation in efficacy studies, and one was evaluated for effects on bacterial peritonitis. Handling characteristics of Oxiplex film were evaluated via laparoscopy.

SETTING

University laboratory.

PATIENT(S)

Rabbits, rats, pigs.

INTERVENTION(S)

Placement of Oxiplex prototypes at the site of injury.

MAIN OUTCOME MEASURE(S)

Mechanical properties, biocompatibility, tissue adherence, adhesion development, infection potentiation, and device handling.

RESULT(S)

Mechanical tests indicated that tensile strength and elongation were inversely correlated. All films tested had excellent tissue adherence properties. Selected films, based on residence time and biocompatibility, prevented adhesion formation in all animals and were highly efficacious in preventing adhesion reformation. The optimal Oxiplex prototype prevented adhesion reformation in 91% of the animals. This Oxiplex film, dyed to allow visualization, prevented adhesion reformation and did not affect bacterial peritonitis. In a laparoscopic model, the Oxiplex film, delivered in FilmSert forceps, via a 5.0-mm trocar, rapidly unfurled and could be easily applied to tissue with strong adherence.

CONCLUSION(S)

These data show development of an adhesion prevention material that is tissue adherent, can be placed via laparoscopy, and does not affect host resistance.

Anti-Kaposi's sarcoma and antiangiogenic activities of sulfated dextrins

Delivery of the sulfated polysaccharide dextrin 2-sulfate by the intraperitoneal route to the lymphatic circulation resulted in a clinically significant improvement in Kaposi's sarcoma in three patients. Our in vitro studies show that although sulfated dextrins do not interfere with the growth of isolated human umbilical vein endothelial cells, they do inhibit the morphological differentiation of endothelial cells into tubes as well as reduce new vessel formation in a placental angiogenesis assay. The antiangiogenic effect of dextrin 6-sulfate is greater than that of dextrin 2-sulfate and is independent of their anti-human immunodeficiency virus type 1 activities.

Assessment of maintenance therapy with reduced doses of PTH(1-34) in combination with a raloxifene analogue (LY117018) following anabolic therapy in the ovariectomized rat

This experiment was designed to evaluate the ability of a raloxifene analogue (RA), LY117018, with or without reduced dosing of human parathyroid hormone (hPTH)(1-34) to maintain gains in bone mass after a fully anabolic treatment regimen given to aging osteopenic rats. Six-month-old rats were ovariectomized (ovx) or sham-operated (sham). After 1 month, ovx rats were treated with an anabolic regimen consisting of subcutaneous hPTH(1-34) 80 microg/kg/day and oral raloxifene 3 mg/kg/day, each given 5 days/week for 3 months. Thereafter, the treated ovx rats went on to an 8 week maintenance phase of treatment with either RA alone at the same dose, hPTH(1-34) at a reduced dosing interval (twice a week), or a combination of the two. Bone mineral density (BMD) was measured ex vivo at four skeletal sites, lumbar spine (L2-4), proximal hemipelvis, whole femur, and tibia, by dual-energy X-ray densitometry. All four sites showed a similar pattern of response. After the 3 month anabolic phase, the sham group had significantly higher BMD values than ovx rats at all skeletal sites (p < or = 0.002). The ovx rats treated with PTH + RA during the anabolic phase of the protocol had significantly higher BMD than the sham group in the femur, tibia, and spine (p < or = 0.02) and higher but not significantly different values in the pelvis. Following the 2 month maintenance phase, comparisons were made with the PTH-RA group at the end of the anabolic phase. Decrements in BMD were seen in all three maintenance therapy groups, but they were not statistically significant in the RA plus reduced PTH dose group. However, reduced hPTH(1-34) dosing and RA alone resulted in significant reductions of bone mass measurements at several skeletal sites during the maintenance phase. We conclude that the raloxifene analogue LY117018 may be useful in maintaining bone mass in aging ovx rats following anabolic therapy with hPTH(1-34) and raloxifene analogue, but that this strategy only allows for dose reduction of hPTH(1-34) rather than its discontinuation.

The addition of a raloxifene analog (LY117018) allows for reduced PTH(1-34) dosing during reversal of osteopenia in ovariectomized rats

To test the hypothesis that an antiresorptive agent might reduce the dosing requirement for an anabolic drug during reversal of osteopenia due to estrogen deficiency, the following experiment was conducted in 6-month-old female rats. Ovariectomy or sham surgery was performed and the following six experimental groups were studied. Untreated (SHAM) or ovariectomized (OVX) animals served as control groups. Four weeks post-OVX, osteopenic rats (now 7 months old), were treated in one of four experimental protocols: human parathyroid hormone (hPTH(1-34)), 80 microg/kg/day, given by subcutaneous injection 5 days/week; a selective estrogen receptor modulator (SERM), raloxifene analog LY117018 (RA), 3 mg/kg/day, given by gavage 5 days/week; and two combinations of LY117018 at the same dose and frequency with hPTH(1-34) (same dose, 5 times/week) and a reduced dosing interval of hPTH(1-34) (same dose, 2 times/week). After 12 weeks of treatment, the four experimental groups were sacrificed at age 10 months. SHAM and OVX controls were also studied at 7 and 10 months of age. Bone mineral density (BMD) was measured by dual-energy X-ray absorptiometry at four skeletal sites: two mixed cortical/trabecular sites (femur and tibia) and two predominantly trabecular sites (lumbar spine and pelvis). The differences in BMD were consistent at all four sites. RA alone maintained BMD at all skeletal sites, but the results were not significantly improved over OVX controls, at age 10 months. hPTH(1-34) injections given 5 days/week resulted in BMD increments significantly higher than in either OVX or SHAM controls (p < 0.001). While the RA did not enhance the anabolic effects of full doses of hPTH(1-34), the addition of RA treatment to twice-weekly hPTH(1-34) dosing resulted in BMD increments at all four skeletal sites that were similar to the more intensive anabolic regimen of hPTH(1-34) therapy given 5 times/week. Therefore, an antiresorptive agent such as SERMs may potentially reduce the pharmacologic doses of PTH needed to reverse estrogen deficiency-induced osteopenia.

Nasotemporal directional bias of V1 neurons in young infant monkeys

PURPOSE

Optokinetic nystagmus (OKN) in young infants typically shows a temporal-to-nasal asymmetry under monocular viewing conditions. The neural basis for this asymmetry has been a matter of debate. One idea is that the OKN asymmetry reflects a similar asymmetry in the directional sensitivity of primary visual cortical (V1) neurons. An alternative hypothesis is that the OKN asymmetry is due to an immaturity in the ability of cortical neurons to influence the activity of subcortical structures that directly control OKN. We addressed this issue by studying the directional sensitivity of V1 neurons in young infant monkeys.

METHODS

The neuronal activity of V1 units was recorded from anesthetized and paralyzed rhesus monkeys ranging in age from 6 days to 8 weeks using standard extracellular single-unit recording methods. For comparison, V1 units from normal adult monkeys were also studied. Using drifting sinusoidal gratings of the optimal spatial frequency and a moderate contrast, we measured the responsiveness of individual units to 24 directions of stimulus movement. The preferred stimulus direction and the magnitude of the directional response bias were determined by a vector summation method.

RESULTS

No clear signs of nasotemporal asymmetries in direction tuning were found in our cell population from infant monkeys. However, the overall directional sensitivity and the peak monocular response amplitudes of these units were significantly lower, and binocular suppression was greater during the first 4 weeks of life than in adults.

CONCLUSIONS

The OKN asymmetry in young infants may be more closely associated with the lower overall directional sensitivity and the subnormal responsiveness of V1 neurons rather than with an obvious asymmetry in the directional properties of V1 neurons.

Reduction of the viral load of HIV-1 after the intraperitoneal administration of dextrin 2-sulphate in patients with AIDS

OBJECTIVE

To determine the safety and efficacy of the sulphated polysaccharide, dextrin 2-sulphate, when delivered to the lymphatic circulation by the peritoneal route.

DESIGN

An open Phase I/II dose-escalation clinical study in which six patients with AIDS were treated with seven courses of dextrin 2-sulphate each lasting 1 month.

METHODS

During each course of treatment, the drug was administered daily for 28 days using an intraperitoneal catheter. Viral load was measured at frequent intervals using a plasma tissue culture infectious dose (TCID) assay, a cellular TCID assay, p24 antigenaemia, HIV-1 RNA and HIV-1 DNA. Plasma beta-chemokine levels were also measured.

RESULTS

Dose escalation was completed without toxicity. A total of 7 patient-months of treatment were completed. With increasing doses of dextrin 2-sulphate, the infectious plasma viraemia, cellular viraemia and p24 antigenaemia all fell during the period of drug administration, but with no significant change in HIV-1 RNA. This was associated with increased plasma levels of macrophage inflammatory protein (MIP)-1alpha and MIP-1beta. Dextrin 2-sulphate accumulated in peritoneal macrophages and induced the release of MIP-1alpha and MIP-1beta from these cells in vitro. These beta-chemokines could have augmented the cell surface-mediated anti-HIV-1 effect of dextrin 2-sulphate in vivo by binding to and blocking the CC-chemokine receptor-5. A second fall in infectious plasma viraemia, cellular viraemia, p24 antigenaemia and HIV-1 RNA was seen at day 100 which was then sustained for several months. A clinical improvement in Kaposi's sarcoma was also seen.

CONCLUSIONS

Our results suggest that the intraperitoneal administration of dextrin 2-sulphate can reduce the replication of HIV-1 in patients with AIDS. With increasing doses of dextrin 2-sulphate, the fall in viral load was seen during the period of drug administration and again 2 months after completing treatment.

Replication and segregation of a miniF plasmid during the division cycle of Escherichia coli

Replication of the miniF plasmid pML31 was examined during the division cycle of Escherichia coli growing with doubling times between 40 and 90 min at 37 degrees C and compared to the replication of plasmid pBR322 and the minichromosome pAL70. The replication pattern of pML31 was indistinguishable from that of pBR322 at all growth rates and very different from the cell-cycle-specific replication of the minichromosome. It is concluded that both pML31 and pBR322 plasmids can replicate at all stages of the division cycle, with a probability of replication that increases gradually, but perhaps not exponentially, during the cycle. In contrast, the modes of segregation of pML31 and pBR322 plasmids into daughter cells at division appeared to differ, raising the possibility that pML31 may segregate in a nonrandom fashion similar to that of chromosomes and minichromosomes.

Perioperative low-molecular-weight heparin. Is it effective and safe

In previous randomised clinical trials of thromboprophylaxis after total hip replacement, low-molecular-weight heparin has been given for an arbitrary 7 to 14 days. The risk factors are mainly perioperative and it is possible that a shorter course may be adequate. We assessed the safety and effectiveness of a three-day course. We assessed 156 primary THR patients after randomisation to either a control group or to receive enoxaparin at 12 hours preoperatively and 12 and 36 hours postoperatively. Thrombosis was diagnosed by routine venography. Haemorrhagic side-effects were assessed by measurement of blood loss, and soft-tissue side-effects by descriptive scores for wound discharge and bruising of the leg. The prevalence of calf thrombosis was 15.4% in the enoxaparin group and 32.1% in the control group (p = 0.01); the prevalence of proximal thrombosis was 15.4% and 17.9% respectively (not significant). There was no difference in haemorrhagic side-effects or wound discharge, but there was more bruising in the enoxaparin group.

Perioperative low-molecular-weight heparin. Is it effective and safe

In previous randomised clinical trials of thromboprophylaxis after total hip replacement, low-molecular-weight heparin has been given for an arbitrary 7 to 14 days. The risk factors are mainly perioperative and it is possible that a shorter course may be adequate. We assessed the safety and effectiveness of a three-day course. We assessed 156 primary THR patients after randomisation to either a control group or to receive enoxaparin at 12 hours preoperatively and 12 and 36 hours postoperatively. Thrombosis was diagnosed by routine venography. Haemorrhagic side-effects were assessed by measurement of blood loss, and soft-tissue side-effects by descriptive scores for wound discharge and bruising of the leg. The prevalence of calf thrombosis was 15.4% in the enoxaparin group and 32.1% in the control group (p = 0.01); the prevalence of proximal thrombosis was 15.4% and 17.9% respectively (not significant). There was no difference in haemorrhagic side-effects or wound discharge, but there was more bruising in the enoxaparin group.

Immunogold localization of GyrA and GyrB proteins in Escherichia coli

Immunogold preparations of Escherichia coli, using anti-GyrA and anti-GyrB antibodies to the subunits of DNA gyrase, showed clear labelling with both secondary antibody and protein A-gold conjugates. Both proteins were located mainly in the cytoplasm, with typically less than 10% in the nucleoid. This partitioning of gyrase proteins between nucleoid and cytoplasm was nonrandom and was consistently observed for a range of different cell preparations. Total gold particle counts were highly variable but suggested levels of at least 1000-3000 molecules per cell for both GyrA and GyrB. Sequential treatment with both anti-GyrA and anti-GyrB monoclonal antibodies resulted in simultaneous labelling of both proteins and revealed no clear association between the two groups of molecules. Treatment of cells with chloramphenicol caused marked changes in nucleoid conformation, but no reduction in cytoplasmic labelling of gyrase proteins. On the assumption that gyrase complexes within the nucleoid are not differentially masked from the monoclonal antibodies, the results obtained in this study suggest that most of the gyrase proteins are not associated with either central nucleoid DNA or cytoplasmic loops of peripheral single-stranded DNA, but are distributed randomly throughout the cytoplasm.

Modifying influence of dehydroepiandrosterone or butylated hydroxytoluene treatment on initiation and development stages of azaserine-induced acinar pancreatic preneoplastic lesions in the rat

Dietary administration of dehydroepiandrosterone (DHEA) (0.6%) or butylated hydroxytoluene (BHT) (1%) during or subsequent to two i.p. injections of azaserine (30 mg/kg body wt) resulted in significant alteration of yield of preneoplastic lesions in both pancreas and liver. While concomitant application appeared not to have any effect on subsequent development of glutathione S-transferase P form (GST-P) positive hepatocellular lesions in either case, BHT and to a lesser extent also DHEA reduced initiation of pancreatic acinar carcinogenesis. Both BHT and DHEA were associated with significant increase in GST-A form positive pancreatic foci when administered after cessation of carcinogen treatment while clearly inhibiting liver lesion development. The results point to a marked differential in the response of the liver and pancreas to external stimulus with regard to preneoplastic focal lesions while demonstrating significant second stage promotion of pancreatic acinar carcinogenesis by BHT and DHEA.

Sex-dependent, tissue-specific opposing effects of dehydroepiandrosterone on initiation and modulation stages of liver and lung carcinogenesis induced by dihydroxy-di-n-propylnitrosamine in F344 rats

Administration of the hormone dehydroepiandrosterone (DHEA) (0.6% in the diet) during or subsequent to injections of the carcinogen dihydroxy-di-n-propylnitrosamine (DHPN) (2 X 1000 mg/kg body weight, i.p.) brought about alteration in the yield of preneoplastic lesions in liver and lung of both male and female F344 rats. Concomitant treatment with DHEA was associated with decrease in the numbers and size of glutathione S-transferase (GST-P)-positive hepatocellular foci while effecting a significant increase in development of lung lesions, especially in females. Long-term treatment with the hormone subsequent to carcinogen exposure brought about a reduction in numbers of liver foci in both sexes but in males was also associated with the development of large GST-P-negative foci and nodules of amphophilic/tigroid cell character. DHEA itself did not induce any focal lesions in the lungs or livers of either sex. Thus the hormone increased sensitivity to 'initiation' in the lung while decreasing that in the liver and exerted a sex-dependent pronounced modulation of the phenotype of a proportion of hepatocellular lesions.